Distinguishing Stocked and Naturally Reproduced Muskellunge Using Pelvic Fin Ray Microchemistry

Otolith microchemistry has been used to distinguish stocked from naturally reproduced fish when natural differences in water chemistry between rearing and stocking locations are present.  However, obtaining otoliths requires sacrificing the fish, which may be undesirable for species such as muskellunge (Esox masquinongy) that are commonly released by anglers and managed for trophy fish.  Fin ray microchemistry represents a non-lethal alternative to otolith analysis that has been demonstrated to be effective for some fish species, but no studies have applied this technique to muskellunge.  We evaluated pelvic fin ray microchemistry as a potential tool for distinguishing stocked from naturally reproduced muskellunge.  Fish and water samples were obtained from hatcheries and lakes with natural differences in water chemistry to determine whether location-specific environmental signatures were recorded in sectioned muskellunge pelvic fin rays, including fish of known environmental history.  Water and fin ray Sr:Ca were strongly correlated.  Three lakes in Illinois possessed Sr:Ca signatures that were distinct from the hatchery where stocked muskellunge are raised, resulting in pronounced shifts in Sr:Ca across sectioned fin rays of stocked fish.  Hatchery and lake-specific Sr:Ca signatures were stable across years.  Individual fish known to have been stocked based on PIT tags implanted at stocking were correctly identified as hatchery-origin fish based on fin ray core Sr:Ca.  Results also indicated that the hatchery Sr:Ca signal can be retained for at least eight years in fin rays of stocked fish.  Fin ray microchemistry represents a new, non-lethal approach for determining environmental history of muskellunge that could be used to assess movement patterns in lake and river systems and the degree to which muskellunge populations are supported by natural reproduction vs. stocking.